The invention relates to an anode structure for cathodic protection against corrosion, having a connecting cable with an electrically insulating covering, the corresponding anode element in the form of an anode or an anode connection having a socket into which the insulation-stripped end of the connecting cable is fitted to form an electrical contact, and the connecting area between connecting cable and anode element being sealed by an electrically insulating seal, the seal being in contact with the covering of the connecting cable, and this seal being surrounded at least partially by a terminal body, and a method for making the anode structure.
European Patent 01 02 380 discloses a metal oxide anode for cathodic protection against corrosion, wherein the anode is configured as a metal oxide anode member in the form of a hollow and substantially cylindrical tube which is open at one end and closed at the opposite end; in the interior this anode has a current receiving interior surface which is plated or coated with an electrically conductive metal or metal alloy, the coating or plating being joined to an electrically conductive cable end member which is fastened at a point that is central relative to the coating or plating; the coating or plating protects the inner surface of the tube with the exception of a relatively narrow area in the upper part of this surface at the open end of the tube, and with the exception of a relatively narrow area at the opposite end of the tube. The centrally fixed cable end member is formed from a bronze spiral. The one open end is sealed by a plastic composition covering the end of the connecting cable.
The seal, especially in the case of a thermosetting casting resin seal, where mechanical tension occurs on account of the absence of a lock between the connecting cable and the anode element, is problematical; moreover, the construction of the spiral structure adjoining the end of the cable covering for contacting purposes is comparatively difficult.
European Patent 84,875 discloses a linear anode structure for cathodic protection against corrosion of elongated metal structures, wherein a power cable provided with electrically insulating covering is connected to the positive pole of a current source and anode segments of valve metal are threaded onto the cable and distributed over its length, which are pinched in sections sealed sleeve-like onto the core of the cable stripped of the covering. This sleeve-like or socket-like portion of the anode segments provided for sealing against the coverings in the transition area is provided with anode surfaces extending star-wise or radially. The application of the anode segments is performed by stripping the electrical cable core in the transitional areas and then applying and crimping a valve-metal sleeve, both the electrically conducting connection to the core and the sealing of the ends of the covering bordering on the transition areas being assured, so that the current transfer area is sealed water-tight from the environment.
Such a system is best used only for elongated objects that are to be protected, such as pipelines, for example, while the cathodic protection from corrosion of other equipment which is exposed to sea water or sunk in the ground, such as small tanks, can be protected only with considerable technical difficulty on account of the great number of anode segments used; also, only those tubes can be used which, if measured in sheet metal or drawn metal or rods are very expensive and have a hard surface that can be coated only poorly.
The invention is addressed to the problem of bringing about a simple, rugged connection between a current-connecting cable and a valve-metal anode which will be suitable for cathodic protection against corrosion not only of compact metal devices but also of a group of metal devices that are exposed to sea water or set in the ground, or can also be used for interior protection. In addition to ease of manufacture, a high reliability and ability to withstand pressure are also to be achieved as regards the transfer of current and moisture-proofing. At the same time, not only tubular anodes, but also anodes of any desired shape are to be able to be connected.
The problem is solved with regard to the apparatus by the fact that the socket is formed in the end of a current feeding pin of the anode element made of valve metal, into which the insulated end of the connecting cable extends, that not only the end of the covering of the connecting cable but also the end of the current feed pin is encompassed by an annular body as seal, consisting of an elastic, electrically insulating material, the pressure in the radial direction required for the sealing being formed by at least one plastically deformable compression collar acting on the seal of the terminal body.
The stability of the seal based on maintaining the flexibility of the seal area proves to be advantageous, so that, in contrast to thermosetting cast resin seals, the seal always holds even when the operating pressure or the working temperature changes, and the formation of gaps between the cast resin and the workpiece can be reliably prevented. The electrical connection can be exposed to a working pressure of up to 25 bar.
It has proven to be especially advantageous to provide an annular body of rubber, especially of neoprene, since then working temperatures up to 90.degree. C. can be employed without losing the seal.
An additional advantage is to be seen in the fact that not only compact single objects can be protected against cathodic corrosion, but also branched systems, such as tanks in refineries can be protected, due to the possibility of branching the current connecting cables. The working pressure acting on the seal can amount to as much as 20 bar.
At the same time the possibility of making the connection in conventional manufacturing apparatus by means of arbor presses and drawing methods proves to be advantageous.
Another advantage is to be seen in the fact that the current connecting pin can be made on the one hand as a component of the anode, but on the other hand it serves only the current-carrying function, while the actual anode is remote from the junction and thus can be made as an anode in any desired form.